Anti-skid braking control device including cam and oppositely disposed, reciprocating pistons

ABSTRACT

An hydraulic anti-skid braking device to produce pulsating or &#34;on and off&#34; operation (intermittent control) of a pair of brakes connected to the front and rear brakes of a motor vehicle. The device includes a pair of pistons each piston including a completely radially extending through-passage, and off-set and bleed portions.

BACKGROUND OF THE INVENTION

The present invention relates to hydraulic anti-skid braking systems forvehicles of the kind in which the vehicle brakes are pulsed or pumped toreduce the possibility of wheel lock-up. The latest and probably mostvaluable invention in the automotive market today is the introduction ofthe anti-lock braking system. It is by far the most important safetyfeature in automobiles today and may be mandatory in the cars oftomorrow as the safety belt today is. The systems installed in today'scars are the more complex versions, where sensors are installed in eachwheel to detect the occurrence of a skid or incipient skid or lock-upcondition. In one example of the prior art, information that sensorsgather causes a high pressure hydraulic pump to reduce the pressure inthe wheel that is just about ready to skid. In this manner, the wheelsare allowed, in a controlled fashion, to be relieved of pressure fromthe brake shoe or pad in order to rotate again, albeit in a very shortperiod of time. As soon as the wheels start to rotate, the computeragain tells the hydraulic pump to apply pressure to the brakes in orderto stop the wheels from rotating. This sequence is repeated normally 4times/second. It is known that the maximum braking action is achievedjust before the wheels skid on a surface. In view of the level ofcomplexity of the devices now being offered in the marketplace of whichapplicant is aware, these "off-the-shelf" devices are not readilyretrofitable on vehicles purchased without one from the factory. Thisdevice being applied for in this application will achieve the sameeffect as the computer controlled one but will perform anti-skid controlin a more economical and retrofitable manner.

The instant invention differs from the prior art in that the instantsystem avoids the complexities of the valving arrangements of the priorart. The simplification is accomplished by reducing the number of partsof the system and by relying upon an improved piston for performing thecritical functions. The instant system is easily retrofitable toexisting automobiles equipped with the conventional tandem hydrauliccylinder.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an improved anti-lockhydraulic brake control system with a pair of unique reciprocatingpistons wherein the "valves" are built into the pistons.

Another object of the present invention of the kind described is toprovide a conventional hydraulic brake system with an easilyretrofittable anti-lock control device wherein the operator of the footbrake pedal does not feel the pulsing or pumping of the brakes as theanti-skid control device is pulsing or pumping the fluid in the brakepressure lines.

It is the intention of the instant system to maintain the wheels at"peak braking" action as long as possible or to keep as many "peaks" aspossible during the process of braking to achieve or maintain themaximum braking without skidding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the anti-lock brake control device ofthe instant invention in a dual brake system. The right side of FIG. 1depicts the position of a piston when the brakes are activated while theleft side of FIG. 1 depicts the non-aligned position of a piston wherethe pressure in the wheel brake is being relieved.

FIG. 2 is view of hydraulic piston per-se shown in a cutaway view toshow the internal flow passages therein.

COMBINED DESCRIPTION OF THE PREFERRED EMBODIMENT AND MODE OF OPERATION

FIG. 1 of the drawing shows a hydraulic brake system with a tandemmaster cylinder 20 with front (B) and rear (A) master cylinders whichare actuated by a brake pedal 19. The anti-skid brake control device 5of the instant invention is installed between the master cylinder 20 andthe rear (R) and front (F) wheel brakes of the motor vehicle. The dualor two-circuit braking system of FIG. 1 includes separate fluid brakecircuits I₁ and I₂ connected to the inlets 13₁ and 13₂ respectively, ofthe hydraulic device. A pair of outlet ports or passages 18₁, and 18₂are connected from the hydraulic anti-lock device 5 to the separatelines 21₁ and 21₂, respectively, of the rear and front brakes circuitsI₁ and I₂ respectively. Each of the piston arrangements generallyindicated at 9₁ and 9₂ of FIG. 1 is substantially identical. Each of thepistons 9₁ and 9₂, in the most forward position, aligns its radiallyextending or through-passages 12₁ and 12₂ with that of the ports 13₁ and13₂ connected to the fluid circuits I₁ and I₂ from master cylinder 20and aligns the noted through-passages 12₁, 12₂ with the output ports18₁, 18₂ to the wheel brakes R and F, respectively. While in thisforward position, the brakes R and F are "on" for a fraction of asecond. Tests have shown that 250 milliseconds is the optimum frequencyfor cycling of the piston assemblies 9₁, 9₂ between open and closedpositions. As is evident from FIG. 1, as the respective piston (9₁ or9₂) moves back from its forward position to its rearward position,through-passage (12₁ or 12₂) within the piston becomes misaligned withthe inlet (13₁,13₂) and outlet (18₁,18₂) ports of the device 5 to thuscut off or isolate the flow of master cylinder fluid to the respectivebrake. As the piston moves further back, the off-set portion of thepiston generally indicated at 14₁,14₂ is exposed to relieve brakepressure from the wheel brakes R,F. Upon the continued movement of thepistons 14₁, 14₂ backward, the piston/expansion chamber 17₁, 17₂enlarges due to the receding piston. The brake fluid from pressure lines21₁, 21₂ of the brakes R,F is evacuated into the expansion chamber 17₁,17₂. The brake fluid from the wheel brakes R,F is evacuated into theexpansion chamber 17₁, 17₂ which is continuously enlarging toaccommodate the volume of the fluid from the wheel brakes R,F. Becausethe fluid is being evacuated from the brake lines 21₁, 21₂ leading fromthe brakes R,F, the pressure to the brakes is relieved.

The cycle of pressurization and evacuation is repeated every 250milliseconds (1/4 second). This frequency of "on/off" of the brakesprecludes the wheels from achieving any lock-up position because thewheels never stay in any position long enough to lock. The oscillatingmotion of the pistons 9₁, 9₂ aligns and misaligns the passages allowingalternate application and release of the brakes, i.e., intermittentbrake supply and release.

The oscillation or reciprocating motions of the pistons are effected bythe revolution of a cam 2. The cam has a lobe (a depression on thewheel) which allows the cam follower (3₁,3₂) to rise up and down on thisdepression on the cam thus pushing the pistons (9₁,9₂) back and forth.The speed of the revolution of the cam determines the speed of theoscillating motion of the pistons. The cam 2 includes a cam shaft or thelike at 4.

In order to preclude excessive loads on the piston seat, the cam, andthe motor, a cam follower (3₁,3₂) is used to rotate freely whileattached to the piston 9₁,9₂ with the cam follower pin 8₁,8₂. In thismanner, the contact points of the cam follower on the cam and the pistonwill be in the form of a rolling motion rather than a "scrubbing" motionwhich would cause premature failure of the cam and piston seat. This isstandard mechanical engineering practice.

In FIG. 2 of the present invention, the expansion flow path C-D isshown. The mechanism used to actuate the cam 2 of the instant inventionis not critical to the invention. Numerous prior art discloses the drivemechanism which forms no part of the invention herein for which a patentis sought. For example, the system may be powered by an electric motorgeared down to improve torque to cause rotation of cam 2 whichalternatetely applies and releases the brakes R,F by the alternateforward and backward motion of the pistons 9₁, 9₂ as the pistonsreciprocate within chambers of the housing 22 of the device 5. Thesystem may be activated by connecting it to the brake light circuit (notshown) so that the system is on every time the brake pedal is applied.Also, the anti-lock brake device 5 of FIG. 1 may be coupled to a sensoror series of sensors with the brake lights so that the system operateswhen the proper combination of events and conditions, as desired, takesplace. The present system is considered to be versatile in that thefrequency of oscillation may be varied by speed or the use of amulti-lobe cam. The frequency may also be variable during usage toconform to road surface conditions with the use of sensors if desired. Ahigher or lower rate of frequency of oscillation may be used dependingon whether the road is asphalt, concrete, gravel, icy, or muddy, or evenwhen days are hot versus cold evenings. The pistons 9₁, 9₂ may be drivento oscillation by an external power source, normally by an externalpower source, normally on a 12 volt electric motor, by vacuum activationor any other appropriate mechanical means not relevant to the presentinvention. The motor shaft is connected to a single lobe cam (ormulti-lobe if preferred) activating the pistons to oscillate back andforth.

With reference to FIG. 2 of the drawing, the piston 9₁ includes multipleports. It should be understood that a description of piston 9₁ alsopertains to the description for corresponding piston 9₂. The piston 9₁includes radially extending port 12₁ and an off-set portion andbleed-off portion generally indicated at 14₁. The bleed-off portion isformed by removing a portion of the periphery of the piston or spoolfrom its periphery which piston slidably engages the inner wall of thechambers within housing 22. The bleed-off portion forms a recess orcavity of indentation which is axially and radially formed. The radialportion extends to a central portion 23 which is concentric with thelongitudinal axis G-H of the piston 9₁. The cavity 23 extends toward butdoes not meet the through-passage or radial port 12₁.

Regarding the operation of the structure of FIGS. 1-2, when a driversteps on the brakes, the master cylinder pressurizes the fluid in thebrake lines causing the brake pads and/or shoes to exert pressure on themotor or brake drums thereby stopping its revolving motion. It should benoted that as the piston 9₁, 9₂ continues its rearward stroke thusincreasing the volume of the expansion chamber 17₁, 17₂ , the retreatingpiston causes a partial vacuum to occur. This partial vacuum allows moreof the brake fluid to be evacuated via 14₁, 23₁, flow path C-D to theexpansion chamber 17₁ so that a portion of the pressure in the brake isrelieved. On the return stroke of the piston 9₁, 9₂, brake fluidaccumulated in the expansion chamber is pushed back into the brake linesby the piston 9₁, 9₂. As the pistons 9₁, 9₂ are cycled back and forth,the brakes are never on and off longer than 1/3 of a second at any timethereby giving the maximum braking action without allowing the wheels toskid. In addition to the above, it should be noted that FIG. 1 includesreturn springs 1₁, 1₂ used to return the pistons 9₁, 9₂ to the normalposition when the brakes are off and when the anti-skid system is not inoperation. The return springs 1₁, 1₂ are located inside thepiston/expansion chamber 17₁, 17₂ defined by the end of the piston headof pistons 9₁, 9₂ and the abutment members 18₁, 18₂ of the end caps 7₁,7₂. Screws 6 hold the end caps 7₁,7₂ in place. The cam 2 is of thesingle lobe type with a slow rise designed to minimize the load on thedrive motor (not shown) when the device 5 is working. Elements 3₁, 3₂are cam followers used to minimize the load on cam 2 during its cyclingoperation by its rolling motion. The cam 2 of FIG. 1 includes a motorshaft 4 fixed to the cam by a pin to a effect turning motion when themotor (not shown) is on. The high pressure end caps 7₁, 7₂ are used toseal off the brake fluid from each end of the anti-skid housing 22. Theend caps 7₁, 7₂ hold the return springs 1₁, 1₂ in place via abutments18₁, 18₂ thereof. Each of the cam followers 3₁, 3₂ includes a respectivecam follower pins 8₁, 8₂ for attaching the cam follower to itsrespective piston.

FIG. 1, in addition, includes O-ring and O-ring grooves at 10₁, 10₂wherein these O-rings inside the grooves are used to keep the brakefluid contained. Similarly, the portions 18₁, 18₂ of the end caps 7₁, 7₂include O-rings/grooves at 11₁, 11₂. Inlets 13₁, 13₂ of the device 5 areconnected to brake circuits I₁, I₂ by conventional brake line fittingsor couplings.

I claim:
 1. An anti-lock hydraulic brake control device (5) including apair of inlet ports (13₁,13₂) connected to a pair of brake circuits(I₁,I₂) from separate outlets of a tandem master cylinder (20) actuatedby a brake pedal (19), the device (5) including within its housing (22)a pair of alternately reciprocating pistons (9₁,9₂) with pin-connectedcam followers (3₁,3₂) attached thereto, the followers situated foralternate engagement with a driven cam (2) located between said camfollowers (3₁,3₂), each of said pistons (9₁,9₂) including a respectivecompletely radially oriented through-passage (12₁,12₂) adapted in oneforward position to register in fluid alignment the respective inletport (13₁,13₂) of the device (5) and an outlet port (18₁,18₂) connectedto rear (R) and front (F) brakes of the vehicle respectively and adaptedin a second rearward position to isolate the said inlet port (13₁,13₂)from fluid communication with the through-passage (12₁,12₂), each piston(9₁,9₂) also including therein off-set and bleed off configurations orportions for relieving brake pressure from the outlet port (18₁, 18₂)comprising an axially and radially flow-through passageway (D-C)partially formed by an elongated groove or recess or indentation in theouter periphery of the piston which passageway leads to a central reliefchamber or cavity (23₁,23₂) in the piston, the off-set and bleed offportions of the piston (9₁,9₂) and its cavity being configured toconnect the respective brake (R,F) to an associated piston/expansionrelief or release chamber (17₁,17₂) situated between one end of saidrespective piston (9₁,9₂) and an abutment (18₁,18₂) of a respective endcap (7₁,7₂) of the single housing (22) of the brake control device (5),wherein each of said pistons (9₁,9₂) directly slides on an innerperipheral chamber surface within a chamber of said housing (22) and isof a single, one-piece construction with the supply through-passage(12₁,12₂) being axially spaced by a predetermined amount from theoff-set portion of the respective piston (9₁,9₂), each saidpiston/expansion chambers (17₁,17₂) including a respective coil spring(1₁, 1₂) with opposite ends located within said respective abutment(18₁,18₂) of the said respective end cap (7₁,7₂) and a recess of theother end of the respective said piston (9₁,9₂), wherein rotation ofsaid cam (2) causes alternate application and release of the respectivebrakes (R,F) by one of said brakes being applied by appropriatealignment of the through-passage (12₁,12₂) and respective brake with thesupply inlet port (13₁,13₂) while the other brake is being released byappropriate alignment of the other brake to the piston/expansion chamber(17₁,17₂) after the supply inlet port (13₁,13₂) of the associated otherbrake has been isolated from the through-passage (12₁,12₂) by slidingmovement of the piston away from the position in which thethrough-passage is open to the master cylinder.